This invention relates to multi-speed planetary transmissions for use in vehicles and, more particularly, to multi-speed planetary transmissions having six or more forward speed ratios.
Passenger vehicles include a powertrain that is comprised of an engine, multi-speed transmission and a differential or final drive. The multi-speed transmission increases the overall operating range of the vehicle by permitting the engine to operate through its torque range a number of times. The number of forward speed ratios that are available in the transmission determines the number of times the engine torque range is repeated. Early automatic transmissions had two speed ranges. This severely limited the overall speed range of the vehicle and therefore required a relatively large engine that could produce a wide speed and torque range. This resulted in the engine operating at a specific fuel consumption point, during cruising, other than the most efficient point. Therefore, manually shifted (countershaft transmissions) were the most popular.
With the advent of three and four speed automatic transmissions, the automatic shifting (planetary gear) transmission increased in popularity with the motoring public. These transmissions improve the operating performance and fuel economy of the vehicle. The increased number of speed ratios reduces the step size between ratios and therefore improves the shift quality of the transmission by making the ratio interchanges substantially imperceptible to the operator under normal vehicle acceleration. It has been suggested that the number of forward speed ratios be increased to five and even six speeds. This has been accomplished in many heavy truck powertrains. Six-speed transmissions are disclosed in U.S. Pat. No. 4,070,927 issued to Polak on Jan. 31, 1978, and U.S. Pat. No. 6,071,208 issued to Koivunen on Jun. 6, 2000.
The Polak transmission provides six forward speed ratios. Six-speed transmissions offer several advantages over four-speed transmissions, including improved vehicle acceleration and improved fuel economy. While many trucks employ power transmissions, such as Polak, having six or more forward gear ratios, passenger cars are still manufactured with three- and four-speed automatic transmissions and relatively few five or six-speed devices due to the size and complexity of these transmissions. The Koivunen patent utilizes six torque transmitting devices including four brakes and two clutches to establish the six forward speed ratios and one reverse ratio.
It is an object of the present invention to provide an improved planetary transmission having three planetary gear sets to establish at least six forward speed ratios.
In one aspect of the present invention, the planetary transmission has three interconnected planetary gear sets. In another aspect of the present invention, the planetary gear sets are selectively controlled by five torque transmitting mechanisms to produce at least six forward speed ratios and one reverse ratio. In yet another aspect of the present invention, the torque transmitting mechanisms include at least two clutches and two brakes.
In still another aspect of the present invention, the torque transmitting mechanisms include three clutches and two brakes. In yet still another aspect of the present invention, the torque transmitting mechanisms include two clutches and three brakes. In still yet another aspect of the present invention, the three planetary gear sets are continuously interconnected through one member of each planetary gear set to provide three interconnected members. In still yet another aspect of the present invention, two adjacent planetary gear sets are continuously interconnected through another member of each planetary gear set to provide two interconnected members. In a further aspect of the present invention, at least one planetary gear set has a member continuously connected with an input shaft. In a further aspect of the present invention, at least one planetary gear set has a member continuously connected with an output shaft.
In yet a further aspect of the present invention, one of the torque transmitting mechanisms selectively connects a member of one of the planetary gear sets with the input shaft, and another of the torque transmitting mechanisms selectively interconnects one member in each of two of the planetary gear sets. In a still further aspect of the present invention, a further of the torque transmitting mechanisms is selectively operable to connect the three continuously interconnected planetary gear members with a stationary housing. In yet still a further aspect of the present invention, each of the planetary gear sets is a simple planetary gear set wherein only a single pinion mesh is present between the sun gear member and the ring gear member. In yet still another aspect of the present invention, at least one of the planetary gear sets has intermeshing pinion gear members that mesh with the sun gear member and the ring gear member, respectively.
The present invention is embodied in a family of transmissions that provide low mechanical content and low cost in a six-speed planetary transmission mechanism. Each family member has three planetary gear sets that are serially arranged and interconnected to form a planetary gear arrangement. The planetary gear sets may each be of the single pinion type or double pinion type. In either event, each planetary gear set has three rotatable members, namely a sun gear member, a ring gear member, and a planet carrier assembly member. One member of each of the three planetary gear sets are continuously interconnected; in other words, three members are interconnected. Another member in each of two adjacent planetary gear sets are also continuously interconnected; in other words, two members are interconnected. At least one member of one of the planetary gear sets is continuously connected with an input shaft and at least one member of another of the planetary gear sets is continuously connected with an output shaft. The transmissions include five torque transmitting mechanisms that are selectively operable in combinations of two to establish six forward speeds and a reverse speed.
A first of the torque transmitting mechanisms selectively connects a member of a first or second of the planetary gear sets to a stationary transmission member, such as a housing, and a second of the torque transmitting mechanisms selectively connects the second or a third of the planetary gear sets with the stationary transmission member. A third and a fourth of the torque transmitting mechanisms each selectively interconnects a member of the third planetary gear set with a member of the first or second planetary gear set. A fifth of the torque transmitting mechanisms selectively connects a member of one of the planetary gear sets to the stationary member or, in the alternative, the fifth of the torque transmitting mechanisms connects a member of one of the planetary gear sets with one member of one or more of the planetary gear sets.